The rapid identification of key suspects is an important aspect of a crime investigation. The crime scene requires that the law enforcement officers rapidly separate suspects from witnesses. When a shooting is involved, the officers must identify the shooter and eliminate others. Gunpowder residue contains characteristic particulates, morphological and elemental, that can be identified at forensics laboratories by sophisticated equipment and analysis. The laboratories are remotely located and heavily contracted, and days might elapse before determinations can be made, obviously hampering the ability to solve the shooting.
One of the first tests for more rapidly identifying and eliminating potential suspects in a shooting incident involved melted paraffin that was poured on a suspect's hands and allowed to harden. Thereafter, the cast was removed and sprayed with a chemical solution to identify residue. These tests convert nitrocellulose and nitroglycerine into nitrates, presumptively associated with gunpowder residue, that develop distinctive coloration in the solution. The tests could be performed locally but not conveniently in the field. Later, chemical tests were developed for trace elements in gunpowder residue, i.e. antimony, lead and barium. These elements are not commonly found in nature, reducing extraneous nitrate presence, and changed to a distinctive color in the presence of a developing solution. These test were also laboratory based and resulted in delays between testing and identification. While the foregoing provided useful in ultimately determining the shooter from a group of subjects, valuable time was lost in the investigation.
Scanning electron microscopes have also been used to provide greater certainty in the identification process and for use as probative evidence, but the expense of the equipment and specialized personnel place the test beyond the means of most law enforcement agencies for screening purposes, and where used for screening added considerable time to the identification process, thereby limiting their usefulness in most investigations.
To enable investigators to make gunpowder residue determinations in the field for presumptive screening, a number of kits are available using chemical reagents. After swabs or patches have removed residues from the subjects, the reagents are poured from containers onto the swabs and patches. After a short period, the gunpowder residues take on a distinctive coloration, indicating the presumptive presence of gunpowder particulates. Accepted reagents have included diphenylamine and sodium rhodizonate. These field tests, while enabling field personnel to quickly screen plural subjects for presumptive evidence, require exposure to the chemical reagents. The reagents generally contain concentrated acids that can be hazardous if improperly handled, causing skin burn on contact and degradation of organic material including clothing. Moreover, the disposal of the chemicals and test supplies also presents problems. It has accordingly be deemed desirable in the law enforcement field to provide a field test kit for the screening of potential suspects for gunpowder residues that is safe, quick, accurate and inexpensive to use by ordinary law enforcement personnel.